A continuing trend in semiconductor integrated circuit manufacturing is to make more powerful and complex integrated circuit devices in a smaller area. Manufacturers achieve this objective by making individual circuit component sizes smaller and by locating these components closer together. Millions of active and passive circuit components, such as transistors, capacitors, and resistors are formed on a semiconductor substrate. These circuit components are formed electrically isolated from each other on the substrate and later are interconnected to form functional circuits. The quality of these interconnecting structures greatly affects the performance, and reliability of the completed integrated circuits.
Often the interconnections are fabricated as a multilayer structure having alternating layers of patterned metallic and dielectric materials. The dielectric layers, frequently a form of silicon oxide, serve to separate the conductors, both vertically and horizontally, and very small, vertical metal filled vias in the dielectric layers provide a means of interconnection between the metal levels.
In multilevel structures, the metal conductors may include a base or seed layer, a bulk conductor layer, a capping layer, and a barrier layer, and the sum of these layers is referred to as a metal stack. The metal stack is formed on a dielectric layer and then etched, through the use of photolithographic techniques, to define the interconnecting structure.
A typical via structure formed on a horizontal metal interconnection layer stack includes a via hole through one or more dielectric layers, and a conductive metallic plug system in the via hole.
At present, Aluminum and aluminum alloys are widely used as the bulk conductors, and tungsten is widely used as the metal plug for the via in the art of integrated circuit manufacturing.
Structural defects in the system of the interconnecting metal layer stack and the metallic plug in the vias can cause performance and reliability problems in the projected life span of the semiconductor integrated circuit device. One structural defect manifests itself in the form of voids at the interface region between the metallic plug and the metal stack. Application Ser. No. 10/091,789 identifies one root cause of void formation in a tungsten/aluminum system and the solution to the cause. In that invention, a process is described to arrest the metal intrusion from the metal stack into the vias. Application Ser. No. 10/091,789 is hereby incorporated by reference in its entirety.
In this invention, Applicants identify another cause of void formation at the interface of the tungsten plugs and the aluminum metal stack and describes a solution to eliminate or to reduce its harmful effect.